In recent years, scroll compressors that use refrigerant such as HFO refrigerant having a global warming potential (GWP) lower than the conventional HFC refrigerant have been developed in view of preventing global warming. Typical examples of HFO refrigerant include 2,3,3,3-tetrafluoro-1-propene. However, since HFO refrigerant has low refrigeration capacity per unit volume, the scroll compressor is required to have an increased suction volume to ensure refrigeration capacity equivalent to the refrigeration capacity when using the conventional HFC refrigerant. Accordingly, there is a known technique for increasing a suction volume by increasing a stroke volume of the compressor by use of an asymmetrical spiral structure in which a winding angle of a stationary scroll wrap that constitutes a compression chamber is formed to be larger than a winding angle of an orbiting scroll wrap (for example, see Patent Literature 1).
However, in the case where a single-component refrigerant of HFO refrigerant, which typically includes 2,3,3,3-tetrafluoro-1-propene, or a mixed refrigerant that contains HFO refrigerant is used in a scroll compressor having an asymmetrical spiral structure, a discharge temperature of refrigerant after compression may increase depending on operation conditions, which may cause deterioration of refrigerating machine oil and lead to a failure of the scroll compressor.
Accordingly, there is a known technique for injecting refrigerant of an intermediate pressure into a compression chamber via one injection port to cool and lower a discharge temperature and thereby to improve reliability while improving efficiency by reducing a work load (see, for example, Patent Literature 2).
According to Patent Literature 2, in a scroll compressor having an asymmetrical spiral structure, one injection port for injecting refrigerant of an intermediate pressure into a compression chamber is provided on a base plate of a stationary scroll at a position satisfying the following conditions (1) to (3) to increase an injection flow rate and thereby improve efficiency.
(1) The position where the injection port opens to a compression chamber having a large sealing volume and a compression chamber having a small sealing volume in sequence and allows for sequential injection into these two compression chambers.
(2) The position where the injection amount into the compression chamber having a small sealing volume is larger than the injection amount into the compression chamber having a large sealing volume.
(3) The position located in an outer region of a line that is offset from an outer line of the stationary scroll wrap by a thickness of the orbiting scroll wrap and in an inner region of a line that is offset from an inner line of the stationary scroll wrap by a thickness of the orbiting scroll wrap, and where injected refrigerant does not leak into a suction side.